time907356

Hi - I searched a bit before posting, but didn't see any similar topics. We're still 'getting to know' our 911 a bit, but this issue seems out of whack. Basically, sometimes the heater works, sometimes it doesn't. We have the automatic controls (no levers), the dash sensor, and the 0-10 dial behind the e-brake.
It seems like it'll work, but after using the air conditioner (climate is changing rapidly in SC this year...) the heater doesn't work for a while. This goes back to when we bought the car. Drove it from PA to SC, and it didn't work for ~5hrs, then it just started working without any warning during the trip!
I haven't done any diagnostics yet, except for the plug in the engine compartment blower; it's attached!!
Any suggestions where to start??

irobertson

Could be your flapper boxes (or actuation cables) are seized up a bit and the little motor that operates them is having a hard time making them move. Or it could be something whacky with your cabin temp sensor. If it is intermittent, then the automatic heat will fluctuate wildly.
There is a trouble shooting section in the Bently book if you have one.
Electrical measurements and such.
You can also open up the centre console and verify movement of the flapper box cables as you turn the heat up and down.

time907356

Thanks for the feedback. I have the bently manual, so I'll give it a read. The heater started working agiain yesterday morning, on the way home from Church! Nice and toasty when it works. The seats are coming out for a carpet replacement soon, so the list of investigatory items is growing...including why the seats won't glide back!!

downtownab

It's because God favored you for going to church.

1986 Targa

All of the above are good ideas.

However, can you be more specific?

Such as, are you losing airflow?

Or heat?

Hope this helps:

1. Check and clean the fuse holders.

2. Check the footwell blower relay.

pm me as needed.

Good luck,

Gerry

kazbah2

I have a 1987 911 and it doesn't have auto-heat. But more than once, I've had a problem with the blower motors. So, I've improved a previous poster (full credit to them) as a really simplified view of how the blower motors work and are configured. First, to understand how they work:

Foot well blowers will only work if:
1. The Engine Compartment Controller "senses" the rear engine blower running.
2. The Engine Compartment Controller provides 12VDC to the heater switch
3. The Blowers then receive power thru one of two ways
3.1 Thru the heater switch (1,2), thru the resister assembly providing speeds low, medium
3.2 Thru the heater switch 3, which provides ground to the Aux Blower Relay
3.3 And with 3.2 energized, the Aux Blower Relay Contact via fuse 2 provides 12 VDC to the motors/high

And concerning the heater switch (mine is not auto heat, but 4 positions: off, low, medium, high)
Heater switch positions (mutually exclusive, only one position is active at a time)
0 nothing
1 provides 12vdc to the resistor low speed
2 provides 12vdc to the resistor assembly medium speed
3 provides ground to the aux blower relay
kz